Method of process optimization for dual tone development

ABSTRACT

A method for patterning a substrate is described. In particular, the invention relates to a method for double patterning a substrate using dual tone development. Further, the invention relates to optimizing a dual tone development process.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to co-pending U.S. patent application Ser.No. 12/______, entitled “METHOD OF PATTERNING A SUBSTRATE USING DUALTONE DEVELOPMENT” (TEE-006), filed on even date herewith. The entirecontent of this application is herein incorporated by reference in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for patterning a substrate. Inparticular, the invention relates to a method for double patterning asubstrate using dual-tone development.

2. Description of Related Art

In material processing methodologies, such as those used in thefabrication of micro-electronic devices, pattern etching is oftenutilized to define the intricate patterns associated with variousintegrated circuit elements. Pattern etching comprises applying apatterned layer of radiation-sensitive material, such as photo-resist,to a thin film on an upper surface of a substrate, and transferring thepattern formed in the layer of radiation-sensitive material to theunderlying thin film by etching.

The patterning of the radiation-sensitive material generally involvescoating an upper surface of the substrate with a thin film ofradiation-sensitive material and then exposing the thin film ofradiation-sensitive material to a pattern of radiation by projectingradiation from a radiation source through a mask using, for example, aphotolithography system. Thereafter, a developing process is performed,during which the removal of the irradiated regions of theradiation-sensitive material occurs (as in the case of positive-tonephoto-resist), or the removal of non-irradiated regions occurs (as inthe case of negative-tone photo-resist). The remainingradiation-sensitive material exposes the underlying substrate surface ina pattern that is ready to be etched into the surface.

As an example, for positive-tone pattern development, a typicallithographic patterning technique is shown in FIGS. 1A and 1B. As shownin FIG. 1A, a layer of positive-tone photo-resist 102 is formed on asubstrate 101. The layer of photo-resist 102 is exposed toelectromagnetic (EM) radiation 107 through a mask 103. Mask 103 includestransparent portions 104 and opaque features 108 that form a pattern, asshown in FIG. 1A. A distance (or pitch) 109 between opaque features 108is shown in FIG. 1A. The transparent portions 104 transmit EM radiation107 to the layer of positive-tone photo-resist 102, and the opaquefeatures 108 prevent EM radiation 107 from being transmitted to thelayer positive-tone photo-resist 102. FIG. 1A shows the layer ofpositive-tone photo-resist 102 having exposed portions 105 that areexposed to EM radiation 107 and unexposed portions 106 that are notexposed to EM radiation 107. As shown in FIG. 1A, mask features 108 areimaged onto the layer of positive-tone photo-resist 102 to producecorresponding photo-resist features aligned with unexposed portions 106.

As shown in FIG. 1B, after removing exposed portions 105 of the layer ofpositive-tone photo-resist 102, unexposed portions 106 remain onsubstrate 101 and form the pattern transferred from mask 103 tosubstrate 101. As shown in FIGS. 1A and 1B, mask features 108 are imagedonto the layer of positive-tone photo-resist 102 to producecorresponding photo-resist features (i.e., unexposed portions 106). Asshown in FIGS. 1A and 1B, pitch 110 between unexposed portions 106 isdetermined by pitch 109 between features 108 of mask 103.

As another example, for negative-tone pattern development, a typicallithographic patterning technique is shown in FIGS. 2A and 2B. As shownin FIG. 2A, a layer of negative-tone photo-resist 202 is formed on asubstrate 201. The layer of negative-tone photo-resist 202 is exposed tothe EM radiation 207 through a mask 203. The mask 203 includestransparent features 204 that form a pattern and opaque portions 208, asshown in FIG. 2A. A distance (pitch) 209 between transparent features204 is shown in FIG. 2A. Transparent features 204 transmit EM radiation207 to the layer of negative-tone photo-resist 202, and opaque portions208 prevent EM radiation 207 from being transmitted to the layer ofnegative-tone photo-resist 202. FIG. 2A shows the layer of negative-tonephoto-resist 202 having exposed portions 205 that are exposed to EMradiation 207 and unexposed portions 206 that are not exposed to EMradiation 207. As shown in FIG. 1A, mask features 204 are imaged ontothe layer of negative-tone photo-resist 202 to produce correspondingphoto-resist features aligned with exposed portions 205.

As shown in FIG. 2B, after removing unexposed portions 206 of the layerof negative-tone photo-resist 202, exposed portions 205 remain onsubstrate 201 and form a pattern transferred from mask 203 to substrate201. As shown in FIGS. 2A and 2B, mask features 204 are imaged onto thelayer of negative-tone photo-resist 202 to produce correspondingphoto-resist features (i.e., exposed portions 205). Pitch 210 betweenexposed portions 205 is determined by pitch 209 between features 204 ofmask 203, as shown in FIGS. 2A and 2B. Photolithographic systems forperforming the above-described material processing methodologies havebecome a mainstay of semiconductor device patterning for the last threedecades, and are expected to continue in that role down to 32 nmresolution, and less. Typically, in both positive-tone and negative-tonepattern development, the minimum distance (i.e., pitch) between thecenter of features of patterns transferred from the mask to thesubstrate by a lithography system defines the patterning resolution.

As indicated above, the patterning resolution (r_(o)) of aphotolithographic system determines the minimum size of devices that canbe made using the system. Having a given lithographic constant k₁, theresolution is given by the equation

r _(o) =k ₁ λ/NA,  (1)

where λ is the operational wavelength of the EM radiation, and NA is thenumerical aperture given by the equation

NA=n·sin θ_(o).  (2)

Angle θ_(o) is the angular semi-aperture of the photo-lithographysystem, and n is the index of refraction of the material filling thespace between the system and the substrate to be patterned.

Following equation (1), conventional methods of resolution improvementhave lead to three trends in photolithographic technology: (1) reductionin wavelength λ from mercury g-line (436 nm) to the 193 nm excimerlaser, and further to 157 nm and the still developingextreme-ultraviolet (EUV) wavelengths; (2) implementation of resolutionenhancement techniques (RETs) such as phase-shifting masks, and off-axisillumination that have lead to a reduction in the lithographic constantk₁ from approximately a value of 0.6 to values approaching 0.25; and (3)increases in the numerical aperture (NA) via improvements in opticaldesigns, manufacturing techniques, and metrology. These latterimprovements have created increases in NA from approximately 0.35 tovalues greater than 1.35.

Immersion lithography provides another possibility for increasing the NAof an optical system, such as a lithographic system. In immersionlithography, a substrate is immersed in a high-index of refraction fluid(also referred to as an immersion medium), such that the space between afinal optical element and the substrate is filled with a high-indexfluid (i.e., n>1). Accordingly, immersion provides the possibility ofincreasing resolution by increasing the NA (see equations (1), and (2)).

However, many of these approaches, including EUV lithography, RETlithography, and immersion lithography, have added considerable cost andcomplexity to lithography equipment. Furthermore, many of theseapproaches continue to face challenges in integration and challenges inextending their resolution limits to finer design nodes.

Therefore, another trend in photolithographic technology is to utilize adouble patterning approach, which has been introduced to allow thepatterning of smaller features at a smaller pitch than what is currentlypossible with standard lithographic techniques. One approach to reducethe feature size is to use standard lithographic pattern and etchtechniques on the same substrate twice, thereby forming larger patternsspaced closely together to achieve a smaller feature size than would bepossible by single exposure. During double patterning, a layer ofradiation-sensitive material on the substrate is exposed to a firstpattern, the first pattern is developed in the radiation-sensitivematerial, the first pattern formed in the radiation-sensitive materialis transferred to an underlying layer using an etching process, and thenthis series of steps is repeated for a second pattern, while shiftingthe second pattern relative to the first pattern. Herein, the doublepatterning approach may require an excessive number of steps, includingexiting the coating/developing tool and re-application of a second layerof radiation-sensitive material.

Another approach to double the resolution of a lithographic pattern isto utilize a dual-tone development approach, wherein a layer ofradiation-sensitive material on the substrate is exposed to a pattern ofradiation, and then a double pattern is developed into the layer ofradiation-sensitive material by performing a positive-tone developmentand a negative-tone development. However, current dual-tone developmentapproaches lack the ability to adjust, control and/or optimize thedouble pattern formed on the substrate.

SUMMARY OF THE INVENTION

The invention relates to a method for patterning a substrate. Inparticular, the invention relates to a method for double patterning asubstrate using dual tone development. Further, the invention relates tooptimizing a dual tone development process.

According to an embodiment, a method of patterning a substrate to doublethe resolution of a lithographic pattern is described. The patterningprocess utilizes a dual-tone development approach, wherein a layer ofradiation-sensitive material applied to the substrate is exposed to apattern of radiation, and then a double pattern is developed into thelayer of radiation-sensitive material by performing a positive-tonedevelopment followed by a negative-tone development. Furthermore, acritical dimension of the features formed in the double pattern isadjusted, controlled and/or optimized to meet pre-specified patternrequirements that may include a pre-specified critical dimension. Thisadjusting, controlling and/or optimizing include altering any processstep, or altering a combination of steps in the double patterningprocess. For example, the altering of any step or a combination of stepsmay include adding, subtracting, and/or re-ordering the combination ofsteps.

According to another embodiment, a method of optimizing a doublepatterning process is described. The method comprises performing adual-tone development process, and optimizing the dual-tone developmentprocess to achieve a target difference between a target positive-tonecritical dimension and a target negative-tone critical dimension. Thedual-tone development process comprises: exposing a layer ofradiation-sensitive material to a pattern of radiation, performing apositive-tone development process to remove a first radiation-sensitivematerial portion characterized by a positive-tone critical dimension,and performing a negative-tone development process to remove a secondradiation-sensitive material portion characterized by a negative-tonecritical dimension. The optimization of the dual-tone developmentprocess comprises: acquiring one or more positive-tone characteristics,the one or more positive-tone characteristics relate the positive-tonecritical dimension to a control parameter for a first set of processparameters; acquiring one or more negative-tone characteristics, the oneor more negative-tone characteristics relate the negative-tone criticaldimension to the control parameter for a second set of processparameters; selecting a target positive-tone characteristic from the oneor more positive-tone characteristics that approximately intersects thetarget positive-tone critical dimension at a target control parameter towithin a first deviation; selecting a target negative-tonecharacteristic from the one or more negative-tone characteristics thatapproximately intersects the target negative-tone critical dimension atthe target control parameter to within a second deviation; andestablishing a process recipe for performing the dual-tone developmentprocess using the target positive-tone characteristic, the targetnegative-tone characteristic, and the target control parameter.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B illustrate a lithographic patterning technique utilizinga positive-tone photo-resist according to the prior art;

FIGS. 2A and 2B illustrate a lithographic patterning technique utilizinga negative-tone photo-resist according to the prior art;

FIG. 3 illustrates a method of patterning a substrate according to anembodiment;

FIGS. 4A through 4D illustrate a method of patterning a substrateaccording to another embodiment;

FIG. 5 illustrates a method of patterning a substrate according toanother embodiment;

FIG. 6 illustrates a method of patterning a substrate according toanother embodiment;

FIG. 7 illustrates a method of patterning a substrate according toanother embodiment;

FIG. 8 presents exemplary data for patterning a substrate;

FIG. 9 presents exemplary data for patterning a substrate;

FIG. 10 presents additional exemplary data for patterning a substrate;

FIG. 11 presents additional exemplary data for patterning a substrate;and

FIG. 12 illustrates a method of patterning a substrate according to yetanother embodiment.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

A method for patterning a substrate is disclosed in various embodiments.However, one skilled in the relevant art will recognize that the variousembodiments may be practiced without one or more of the specificdetails, or with other replacement and/or additional methods, materials,or components. In other instances, well-known structures, materials, oroperations are not shown or described in detail to avoid obscuringaspects of various embodiments of the invention.

Similarly, for purposes of explanation, specific numbers, materials, andconfigurations are set forth in order to provide a thoroughunderstanding of the invention. Nevertheless, the invention may bepracticed without specific details. Furthermore, it is understood thatthe various embodiments shown in the figures are illustrativerepresentations and are not necessarily drawn to scale.

Reference throughout this specification to “one embodiment” or “anembodiment” or variation thereof means that a particular feature,structure, material, or characteristic described in connection with theembodiment is included in at least one embodiment of the invention, butdo not denote that they are present in every embodiment. Thus, theappearances of the phrases such as “in one embodiment” or “in anembodiment” in various places throughout this specification are notnecessarily referring to the same embodiment of the invention.Furthermore, the particular features, structures, materials, orcharacteristics may be combined in any suitable manner in one or moreembodiments. Various additional layers and/or structures may be includedand/or described features may be omitted in other embodiments.

Various operations will be described as multiple discrete operations inturn, in a manner that is most helpful in understanding the invention.However, the order of description should not be construed as to implythat these operations are necessarily order dependent. In particular,these operations need not be performed in the order of presentation.Operations described may be performed in a different order than thedescribed embodiment. Various additional operations may be performedand/or described operations may be omitted in additional embodiments.

Methods for patterning a substrate, including methods to reduce theminimum pitch of a pattern that can be transferred onto a substrate fora given lithographic tool and mask, are described herein. Multiplechemical treatments on exposed radiation-sensitive materials, such asphoto-resist, are used to achieve a reduction in a lithographic pitch ofabout a factor of two.

According to an embodiment, a method of patterning a substrate to doublethe resolution of a lithographic pattern is described. The patterningprocess utilizes a dual-tone development approach, wherein a layer ofradiation-sensitive material applied to the substrate is exposed to apattern of radiation, and then a double pattern is developed into thelayer of radiation-sensitive material by performing a positive-tonedevelopment followed by a negative-tone development. Furthermore, acritical dimension of the features formed in the double pattern isadjusted, controlled and/or optimized to meet pre-specified patternrequirements that may include a pre-specified critical dimension. Thisadjusting, controlling and/or optimizing include altering any processstep, or altering a combination of steps in the double patterningprocess. For example, the altering of any step or a combination of stepsmay include adding, subtracting, and/or re-ordering the combination ofsteps.

FIG. 3 illustrates a method of transferring a pattern from a mask onto asubstrate according to one embodiment. A layer of radiation-sensitivematerial 302, such as photo-resist, is formed on a substrate 301, andthen it is exposed to radiation 320 from a radiation source of alithography system (not shown) using a mask 303. Mask 303 has opaquefeatures 310 that are periodically spaced at a mask pitch 311 andtransparent portions 304, as shown in FIG. 3.

According to one embodiment, the radiation-sensitive material 302comprises photo-resist. According to another embodiment, theradiation-sensitive material 302 comprises a 248 nm photo-resist, a 193nm photo-resist, a 157 nm photo-resist, or an extreme ultravioletphoto-resist, or a combination of two or more thereof. According toanother embodiment, the radiation-sensitive material 302 comprises apositive-tone photo-resist, or a negative-tone photo-resist. Accordingto another embodiment, the radiation-sensitive material 302 comprises adual-tone photo-resist. A dual-tone photo-resist may be characterized asa photo-resist that behaves as a positive-tone photo-resist or anegative-tone photo-resist depending upon the developing chemistry thatis utilized. According to another embodiment, the radiation-sensitivematerial 302 comprises a photo-resist that switches solubility due to achange in polarity upon exposure to the pattern of radiation and anoptionally elevation of the temperature of the substrate following theexposure. According to another embodiment, the radiation-sensitivematerial 302 comprises a photo-resist that provides acid-catalyzeddeprotection upon exposure to the pattern of radiation and an optionalelevation of the temperature of the substrate following the exposure.

FIG. 3 shows a radiation exposure profile 305 and a resist responseprofile 306 of a response produced in the layer of radiation-sensitivematerial 302 by a pattern of radiation resulting from the projection ofradiation 320 through mask 303 using the lithography system. As shown inFIG. 3, first radiation-sensitive material portions 312 that correspondto transparent portions 304 receive a high radiation exposure fromradiation 320, second radiation-sensitive material portions 313 thatcorrespond to opaque features 310 receive a low radiation exposure fromradiation 320, and third radiation-sensitive material portions 314 thatapproximately correspond to edges of opaque features 310 receive anintermediate radiation exposure from radiation 320. As shown in FIG. 3,the resist response profile 306 corresponding to the firstradiation-sensitive material portions 312 of radiation-sensitivematerial 302 is higher than an upper threshold 308, while the resistresponse profile 306 corresponding to the second radiation-sensitivematerial portions 313 is lower than a lower threshold 309. Further, theresist response profile 306 corresponding to the thirdradiation-sensitive material portions 314 lies between the lowerthreshold 309 and the upper threshold 308.

In one embodiment, when the layer of radiation-sensitive material 302includes a positive-tone photo-resist, resist response profile 306 mayrepresent a chemical concentration of deprotected polymers in the layerof radiation-sensitive material 302 that is approximately proportionalto radiation exposure profile 305, as shown in FIG. 3. In anotherembodiment, when the layer of radiation-sensitive material 302 includesa positive-tone photo-resist, resist response profile 306 may be an acidconcentration in the layer of radiation-sensitive material 302 that isproportional to radiation exposure profile 305. In another embodiment,when the layer of radiation-sensitive material 302 includes anegative-tone photo-resist, resist response profile 306 is an averagepolymer molecular weight in the layer of radiation-sensitive material302 that is proportional to radiation exposure profile 305.

In one embodiment, upper threshold 308 corresponds to a first thresholdof solubility of the layer of radiation-sensitive material 302 when afirst chemistry is applied. In one embodiment, lower threshold 309corresponds to a second threshold of solubility of the layer ofradiation-sensitive material 302 when a second chemistry is applied. Inone embodiment, first radiation-sensitive material portions 312 of thelayer of radiation-sensitive material 302 that correspond to transparentportions 304 that have high radiation exposure in radiation exposureprofile 305 are selectively removed from substrate 301 using a firstchemistry. Second radiation-sensitive material portions 313 of the layerof radiation-sensitive material 302 that have low radiation exposure inthe radiation exposure profile 305 are selectively removed fromsubstrate 301 using a second chemistry. The third radiation-sensitivematerial portions 314 that correspond to approximately the edges ofopaque features 310 that have intermediate exposure in the radiationexposure profile 305 (i.e., radiation exposure between the upperthreshold 308 and the lower threshold 309) remain on substrate 301intact, as shown in FIG. 3. Selectively removing firstradiation-sensitive material portions 312 and second radiation-sensitivematerial portions 313 using different chemistries while leaving thirdradiation-sensitive material portions 314 on substrate 301 intact.

In one embodiment, for first radiation-sensitive material portions 312,resist response profile 306 includes a concentration of acid in thelayer of radiation-sensitive material 302 that is higher than an upperthreshold 308 of acid concentration. In one embodiment, upper threshold308 represents an acid level solubility threshold of the layer ofradiation-sensitive material 302. For example, if an acid concentrationin the layer of radiation-sensitive material 302 is higher than theupper threshold 308 of acid concentration, the layer ofradiation-sensitive material 302 becomes soluble when a first chemistryis applied.

In one embodiment, for second radiation-sensitive material portions 313,resist response profile 306 includes a concentration of acid in thelayer of radiation-sensitive material that is lower than lower threshold309 of acid concentration. In one embodiment, lower threshold 309represents another acid level solubility threshold of the layer ofradiation-sensitive material 302. For example, if acid concentration inthe layer of radiation-sensitive material 302 is lower than lowerthreshold 309 of acid concentration, the layer of radiation-sensitivematerial 302 becomes soluble when a second chemistry is applied.

In one embodiment, the layer of radiation-sensitive material 302includes an upper acid concentration threshold in ranging from about 30%to about 60% of the clear field acid level and a lower acidconcentration threshold ranging from about 10% to about 25% of the clearfield acid concentration. In one embodiment, the clear field acidconcentration is defined as the acid level of the photo-resistcompletely exposed to radiation. In another embodiment, the clear fieldacid concentration is defined as the acid concentration when all the PAG(PhotoAcid Generation) material has reacted with radiation to produceacid species.

Due to diffraction of radiation 320, the third radiation-sensitivematerial portions 314 corresponding to intermediate radiation exposureare created. In one embodiment, third radiation-sensitive materialportions 314 comprise an acid concentration between the upper acidconcentration threshold and the lower acid concentration threshold. Thefirst radiation-sensitive material portions 312 corresponding to highradiation exposure are selectively removed from the substrate using afirst chemistry. The second radiation-sensitive material portions 313corresponding to low radiation exposure are selectively removed from thesubstrate using a second chemistry. The third radiation-sensitivematerial portions 314 corresponding to intermediate radiation exposureremain on substrate 301 to form a pattern transferred by mask 303 andthe lithography system.

As shown in FIG. 3, two photo-resist features (i.e., thirdradiation-sensitive material portions 314) are produced for every onemask feature 310, thereby doubling the amount of the pattern features onsubstrate 301. As a result, feature pitch 319 between the center ofphoto-resist features (i.e., third radiation-sensitive material portions314) becomes twice as small as the mask pitch 311 of the mask 303, asshown in FIG. 3.

Referring now to FIGS. 4A through 4D, a method of patterning a substrateis illustrated according to another embodiment. As illustrated in FIG.4A, a lithographic structure 400 is prepared by forming a layer ofradiation-sensitive material 402 on a substrate 401.

The substrate 401 may comprise a semiconductor, e.g., a mono-crystallinesilicon, germanium, and any other semiconductor. In alternateembodiments, substrate 401 may comprise any material used to fabricateintegrated circuits, passive microelectronic devices (e.g., capacitors,inductors) and active microelectronic devices (e.g., transistors,photo-detectors, lasers, diodes). Substrate 401 may include insulatingmaterials that separate such active and passive microelectronic devicesfrom a conductive layer or layers that are formed on top of them. In oneembodiment, substrate 401 comprises a p-type mono-crystalline siliconsubstrate that includes one or more insulating layers e.g., silicondioxide, silicon nitride, sapphire, and other insulating materials.

As described above, the substrate 401 may comprise a film stack havingone or more thin films disposed between the substrate 401 and the layerof radiation-sensitive material 402. Each thin film may comprise aconductive layer, a non-conductive layer, or a semi-conductive layer.For instance, the thin film may include a material layer comprising ametal, metal oxide, metal nitride, metal oxynitride, metal silicate,metal silicide, silicon, poly-crystalline silicon (poly-silicon), dopedsilicon, silicon dioxide, silicon nitride, silicon carbide, siliconoxynitride, etc. Additionally, for instance, the thin film may comprisea low dielectric constant (i.e., low-k) or ultra-low dielectric constant(i.e., ultra-low-k) dielectric layer having a nominal dielectricconstant value less than the dielectric constant of SiO₂, which isapproximately 4 (e.g., the dielectric constant for thermal silicondioxide can range from 3.8 to 3.9). More specifically, the thin film mayhave a dielectric constant of less than 3.7, or a dielectric constantranging from 1.6 to 3.7.

According to one embodiment, the radiation-sensitive material 402comprises photo-resist. According to another embodiment, theradiation-sensitive material 402 comprises a 248 nm photo-resist, a 193nm photo-resist, a 157 nm photo-resist, or an extreme ultravioletphoto-resist, or a combination of two or more thereof. According toanother embodiment, the radiation-sensitive material 402 comprises apositive-tone photo-resist, or a negative-tone photo-resist. Accordingto another embodiment, the radiation-sensitive material 402 comprises adual-tone photo-resist. According to another embodiment, theradiation-sensitive material 402 comprises poly(hydroxystyrene)-basedresist or a (meth)acrylate-based resist. According to anotherembodiment, the radiation-sensitive material 402 comprises aphoto-resist that switches solubility due to a change in polarity uponexposure to the pattern of radiation and an optionally elevation of thetemperature of the substrate following the exposure. According toanother embodiment, the radiation-sensitive material 402 comprises aphoto-resist that provides acid-catalyzed deprotection upon exposure tothe pattern of radiation and an optional elevation of the temperature ofthe substrate following the exposure.

The layer of radiation-sensitive material 402 may be formed using atrack system. For example, the track system can comprise a Clean TrackACT 8, ACT 12, or Lithius resist coating and developing systemcommercially available from Tokyo Electron Limited (TEL). Other systemsand methods for forming a photo-resist film on a substrate are wellknown to those skilled in the art of spin-on resist technology.

Following the application of the layer of radiation-sensitive material402 to substrate 401, the layer of radiation-sensitive material may bethermally treated in a post-application bake (PAB). For example, atemperature of the substrate may be elevated to about 50 degrees C. toabout 200 degrees C. for a time duration of about 30 seconds to about180 seconds. A track system having post-application substrate heatingand cooling equipment may be used to perform the PAB. For example, thetrack system can comprise a Clean Track ACT 8, ACT 12, or Lithius resistcoating and developing system commercially available from Tokyo ElectronLimited (TEL). Other systems and methods for thermally treating anexposed photo-resist film on a substrate are well known to those skilledin the art of spin-on resist technology.

As shown in FIG. 4B, the layer of radiation-sensitive material 402 isexposed to radiation 407 through a mask 403. The mask 403 comprisesopaque features 410 that prevent radiation 407 from being transmitted tothe layer of radiation-sensitive material 402 and transparent portions404 that transmit the radiation 407 to the layer of radiation-sensitivematerial 402. Mask 403 may include any mask suitable for use in wet ordry lithography, including wavelengths ranging from about 365 nm toabout 13 nm. Mask 403 may include a binary mask or chrome on glass mask.Alternatively, mask 403 may include an alternating phase shift mask, oran embedded phase shift mask.

The exposure of the layer of radiation-sensitive material 402 to thepattern of EM radiation may be performed in a dry or wetphoto-lithography system. The lithography system may be capable ofproviding a pattern of EM radiation at wavelengths of 365 nm, 248 nm,193 nm, 157 nm, and 13 nm. The image pattern can be formed using anysuitable conventional stepping lithographic system, or scanninglithographic system. For example, the photo-lithographic system may becommercially available from ASML Netherlands B. V. (De Run 6501, 5504 DRVeldhoven, The Netherlands), or Canon USA, Inc., Semiconductor EquipmentDivision (3300 North First Street, San Jose, Calif. 95134). Mask 403 canbe illuminated, for example, with normal incident light and off-axisillumination light, such as annular illumination, quadrupoleillumination, and dipole illumination. These methods of illumination andexposing the layer of radiation-sensitive material 402 to radiationusing the mask 403 are known to one of ordinary skill in the art ofmicroelectronic device manufacturing.

As shown in FIG. 4B, radiation 407 is projected through mask 403 to thelayer of radiation-sensitive material 402. The radiation exposure formsone or more first radiation-sensitive material portions 405, one or moresecond radiation-sensitive material portions 406, and one or more thirdradiation-sensitive material portions 408 in the layer ofradiation-sensitive material 402. As shown in FIG. 4B, the one or moresecond radiation-sensitive material portions 406 that correspond toopaque features 410 of mask 403 have low exposure to radiation 407, theone or more first radiation-sensitive material portions 405 thatcorrespond to transparent portions 404 of mask 403 have high exposure toradiation 407, and the one or more third radiation-sensitive materialportions 408 that correspond approximately to the edges of opaquefeatures 410 of mask 403 have an intermediate exposure to radiation 407.The one or more third radiation-sensitive material portions 408 ofintermediate radiation exposure are created because of diffraction ofradiation 407 from the edges of opaque features 410.

In one embodiment, the one or more first radiation-sensitive materialportions 405 corresponding to high radiation exposure receive about 50%or more of radiation 407 incident on substrate 401, the one or moresecond radiation-sensitive material portions 406 corresponding to lowradiation exposure receive less than 15% of the radiation 407 incidenton substrate 401, and the one or more third radiation-sensitive materialportions 408 corresponding to intermediate radiation exposure receivebetween about 15% and about 50% of the radiation 407 incident onsubstrate 401.

In one embodiment, high exposure to radiation 407 increases theconcentration of an acid in the one or more first radiation-sensitivematerial portions 405 to a level higher than an upper acid concentrationthreshold. The upper acid concentration threshold is a first solubilitythreshold of the layer of radiation-sensitive material 402. In oneembodiment, when the concentration of the acid in the one or more firstradiation-sensitive material portions 405 increases to a level higherthan the first threshold of solubility of the layer ofradiation-sensitive material 402 (e.g., acid concentration threshold),the one or more first radiation-sensitive material portions 405 becomesoluble when a first chemistry is applied.

In another embodiment, when the chemical concentration of deprotectedpolymers in the one or more first radiation-sensitive material portions405 increases to a level higher than the first threshold of solubilityof the layer of radiation-sensitive material 402 (e.g., acidconcentration threshold), the one or more first radiation-sensitivematerial portions 405 become soluble when a first chemistry is applied.

In yet another embodiment, when the average polymer molecular weight inthe one or more first radiation-sensitive material portions 405increases to a level higher than the first threshold of solubility ofthe layer of radiation-sensitive material 402, the one or more firstradiation-sensitive material portions 405 become soluble when the firstchemistry is applied.

In the one or more second radiation-sensitive material portions 406corresponding to low radiation exposure, a concentration of an acidand/or chemical concentration of deprotected polymers is less than alower threshold of solubility of the layer of radiation-sensitivematerial 402 (e.g., acid concentration threshold). The one or moresecond radiation-sensitive material portions 406 become soluble when asecond chemistry is applied.

In another embodiment, when the concentration of average polymermolecular weight in one or more second radiation-sensitive materialportions 406 is lower than the second threshold of solubility of thelayer of radiation-sensitive material 402, the one or more secondradiation-sensitive material portions 406 become soluble when the secondchemistry is applied.

Typically, the first solubility threshold and the second solubilitythreshold are determined by a material property of the layer ofradiation-sensitive material 402. The one or more thirdradiation-sensitive material portions 408 corresponding to anintermediate radiation exposure have an acid concentration between aboutthe first solubility threshold and the second solubility threshold. Thatis, the one or more third radiation-sensitive material portions 408 arenot soluble when each of the first chemistry and the second chemistry isapplied to layer of radiation-sensitive material 402.

Following the exposure of the layer of radiation-sensitive material 402to EM radiation, the exposed layer of radiation-sensitive material maybe thermally treated in a post-exposure bake (PEB). For example, atemperature of the substrate may be elevated to about 50 degrees C. toabout 200 degrees C. for a time duration of about 30 seconds to about180 seconds. A track system having post-exposure substrate heating andcooling equipment may be used to perform the PEB. For example, the tracksystem can comprise a Clean Track ACT 8, ACT 12, or Lithius resistcoating and developing system commercially available from Tokyo ElectronLimited (TEL). Other systems and methods for thermally treating anexposed photo-resist film on a substrate are well known to those skilledin the art of spin-on resist technology.

Referring still to FIG. 4B, the one or more first radiation-sensitivematerial portions 405 may be characterized by a first critical dimension420. For example, the first critical dimension may be related to apositive-tone critical dimension following positive-tone developing.Additionally, the one or more second radiation-sensitive materialportions 406 may be characterized by a second critical dimension 422. Asshown in FIG. 4B, the second critical dimension 422 represents an innerdimension of the one or more second radiation-sensitive materialportions 406 (beyond which these portions exist). For example, thesecond critical dimension 422 may be related to a negative-tone criticaldimension following negative-tone developing. Furthermore, the one ormore third radiation-sensitive material portions 408 may becharacterized by a third critical dimension 424. For example, the thirdcritical dimension 424 may be related to a feature critical dimensionfor the features 430 (see FIG. 4D) remaining on substrate 401.

Referring now to FIG. 4C, the one or more first radiation-sensitivematerial portions 405 corresponding to high radiation exposure areselectively removed using a first developing process comprising a firstchemistry. In one embodiment, the first chemistry to selectively removethe one or more first radiation-sensitive material portions 405 includesa base, e.g., alkali, amines, etc. In one embodiment, the firstchemistry to selectively remove the one or more firstradiation-sensitive material portions 405 includes tetramethylammoniumhydroxide (TMAH). In another embodiment, the first chemistry toselectively remove the one or more first radiation-sensitive materialportions 405 includes a base, water, and an optional surfactant.

In one embodiment, substrate 401 having the exposed layer ofradiation-sensitive material 402 is immersed into a development solutioncontaining the first chemistry to remove soluble one or more firstradiation-sensitive material portions 405. Thereafter, the substrate 401is dried. The developing process may be performed for a pre-specifiedtime duration (e.g., about 30 seconds to about 180 seconds), apre-specified temperature (e.g., room temperature), and a pre-specifiedpressure (atmospheric pressure). The developing process can includeexposing the substrate to a developing solution in a developing system,such as a track system. For example, the track system can comprise aClean Track ACT 8, ACT 12, or Lithius resist coating and developingsystem commercially available from Tokyo Electron Limited (TEL).

As shown in FIG. 4C, a first critical dimension 420′ (corresponding tothe one or more first radiation-sensitive material portions 405), asecond critical dimension 422′ (corresponding to the one or more secondradiation-sensitive material portions 406), or a third criticaldimension 424′ (corresponding to the one or more thirdradiation-sensitive material portions 408) may be adjusted, controlled,and/or optimized, as will be discussed below.

As illustrated in FIG. 4C, the one or more second radiation-sensitivematerial portions 406 and the one or more third radiation sensitivematerial portions 408 remain on substrate 401.

Referring now to FIG. 4D, the one or more second radiation-sensitivematerial portions 406 corresponding to low radiation exposure areselectively removed using a second developing process comprising asecond chemistry. In one embodiment, the second chemistry to selectivelyremove the one or more second radiation-sensitive material portions 406includes an organic solvent. In one embodiment, the second chemistry toselectively remove the one or more second radiation-sensitive materialportions 406 includes an organic solvent, optionally water, and anoptional surfactant. In one embodiment, the second chemistry toselectively remove the one or more second radiation-sensitive materialportions 406 includes an alcohol or acetone.

In one embodiment, substrate 401 having the exposed layer ofradiation-sensitive material 402 is immersed into a development solutioncontaining the second chemistry to remove soluble one or more secondradiation-sensitive material portions 406. Thereafter, the substrate 401is dried. The developing process may be performed for a pre-specifiedtime duration (e.g., about 30 seconds to about 180 seconds), apre-specified temperature (e.g., room temperature), and a pre-specifiedpressure (atmospheric pressure). The developing process can includeexposing the substrate to a developing solution in a developing system,such as a track system. For example, the track system can comprise aClean Track ACT 8, ACT 12, or Lithius resist coating and developingsystem commercially available from Tokyo Electron Limited (TEL).

As shown in FIG. 4D, a first critical dimension 420″ (corresponding tothe one or more first radiation-sensitive material portions 405), asecond critical dimension 422″ (corresponding to the one or more secondradiation-sensitive material portions 406), or a third criticaldimension 424″ (corresponding to the one or more thirdradiation-sensitive material portions 408) may be adjusted, controlled,and/or optimized, as will be discussed below.

As illustrated in FIG. 4D, the one or more second radiation-sensitivematerial portions 406 are removed, so that the one or more thirdradiation sensitive material portions 408 remain on substrate 401. Sincean image corresponding to each mask feature (e.g., transparent portions404) has two regions of intermediate radiation exposure (or transitionsregions ranging from low radiation intensity to high radiationintensity), the resulting resist pattern comprises twice the number offeatures 430 than the mask pattern on mask 403. As illustrated in FIG.4D, for every one transparent portion 404 of mask 403, two features 430are produced and a reduced feature pitch 432 between features 430 isachieved.

Pitch 432 between features 430 is less than or equal to about half ofmask pitch 409 between opaque features 410 of mask 403, as shown in FIG.4D. In one embodiment, feature pitch 432 between features 430 may rangefrom about 5 nm to about 30 nm.

The order of the positive-tone development (i.e., development usingfirst chemistry) and the negative-tone development (i.e., developmentusing second chemistry) of the layer of radiation-sensitive material402, as described above with respect to FIGS. 4C and 4D, may beperformed in any order without changing the resulting pattern. In oneembodiment, the one or more first radiation-sensitive material portions405 corresponding to high radiation exposure are selectively removedfrom substrate 401 before removing the one or more secondradiation-sensitive material portions 406 corresponding to low radiationexposure from substrate 401. In another embodiment, the one or morefirst radiation-sensitive material portions 405 corresponding to highradiation exposure are selectively removed from substrate 401 afterremoving the one or more second radiation-sensitive material portions406 corresponding to low radiation exposure from substrate 401.

Referring now to FIG. 5, a flow chart 500 of a method for patterning asubstrate is presented according to an embodiment. Flow chart 500 beginsin 510 when a layer of radiation-sensitive material is formed on asubstrate and, in 520, the layer of radiation-sensitive material isexposed to a pattern of radiation using a mask having a mask criticaldimension to form one or more first radiation-sensitive materialportions, one or more second radiation-sensitive material portions, andone or more third radiation-sensitive material portions. The one or morefirst radiation-sensitive material portions may comprise firstradiation-sensitive material portions subjected to high radiationexposure. The one or more second radiation-sensitive material portionsmay comprise second radiation-sensitive material portions subjected tolow radiation exposure. The one or more third radiation-sensitivematerial portions may comprise third radiation-sensitive materialportions subjected to intermediate radiation exposure characterized by athird critical dimension.

In 530, a temperature of the substrate is optionally elevated to a firstpost-exposure temperature. The thermal treatment process may comprise afirst post-exposure bake (PEB), as described above. The first PEB maycomprise setting the first post-exposure temperature, a time thesubstrate is elevated to the first post-exposure temperature, a heatingrate for achieving the first post-exposure temperature, a cooling ratefor reducing the first post-exposure temperature, a pressure of agaseous environment surrounding the substrate during the elevation ofthe substrate to the first post-exposure temperature, or a compositionof a gaseous environment surrounding the substrate during the elevationof the substrate to the first post-exposure temperature, or acombination of two or more thereof. The first post-exposure temperaturemay be ramped, or stepped.

In 540, the one or more first radiation-sensitive material portions areremoved from the substrate using a first chemistry. The removal of theone or more first radiation-sensitive material portions may becharacterized by a first critical dimension. The removal of the one ormore first radiation-sensitive material portions may be performed usinga first development process, such as a positive-tone development processor a negative-tone development process. The first development processmay comprise setting a composition of the first chemistry, a timeduration for the first development process, or a temperature for thefirst development process, or any combination of two or more thereof.The first chemistry may comprise a base solution. The first chemistrymay further comprise a base solution, water, and an optional surfactant.

In 550, a temperature of the substrate is optionally elevated to asecond post-exposure temperature. The thermal treatment process maycomprise a second post-exposure bake (PEB). The second PEB may comprisesetting the second post-exposure temperature, a time the substrate iselevated to the second post-exposure temperature, a heating rate forachieving the second post-exposure temperature, a cooling rate forreducing the second post-exposure temperature, a pressure of a gaseousenvironment surrounding the substrate during the elevation of thesubstrate to the second post-exposure temperature, or a composition of agaseous environment surrounding the substrate during the elevation ofthe substrate to the second post-exposure temperature, or a combinationof two or more thereof. The first post-exposure temperature may beramped, or stepped.

In 560, the one or more second radiation-sensitive material portions areremoved from the substrate using a second chemistry. The removal of theone or more second radiation-sensitive material portions may becharacterized by a second critical dimension. The removal of the one ormore second radiation-sensitive material portions may be performed usinga second development process, such as a positive-tone developmentprocess or a negative-tone development process. The second developmentprocess may comprise setting a composition of the first chemistry, atime duration for the second development process, or a temperature forthe second development process, or any combination of two or morethereof. The second chemistry may comprise an organic solvent. Thesecond chemistry may further comprise an organic solvent, optionallywater, and an optional surfactant.

In 570, the first critical dimension, the second critical dimension,and/or third critical dimension (corresponding to the critical dimensionof the third radiation-sensitive material portions) are adjusted,controlled and/or optimized to meet pre-specified pattern requirementsthat may include a pre-specified first critical dimension, secondcritical dimension, and/or third critical dimension (corresponding tothe critical dimension of the third radiation-sensitive materialportions). This adjusting, controlling and/or optimizing includealtering the patterning process. The adjusting, controlling, and/oroptimizing is discussed in greater detail below.

The adjusting of the patterning process to achieve a target firstcritical dimension and/or second critical dimension, and/or a targetcritical dimension for the critical dimension of thirdradiation-sensitive material portions comprises performing one or moreof the following: (1) adjusting an exposure dose for the exposing of thelayer of radiation-sensitive material; (2) adjusting the mask criticaldimension for the exposing of the layer of radiation-sensitive material;(3) adjusting the first post-exposure temperature, the time thesubstrate is elevated to the first post-exposure temperature, theheating rate for achieving the first post-exposure temperature, thecooling rate for reducing the first post-exposure temperature, thepressure of a gaseous environment surrounding the substrate during theelevation of the substrate to the first post-exposure temperature, or acomposition of the gaseous environment surrounding the substrate duringthe elevation of the substrate to the first post-exposure temperature,or a combination of two or more thereof; (4) adjusting the secondpost-exposure temperature, the time the substrate is elevated to thesecond post-exposure temperature, the heating rate for achieving thesecond post-exposure temperature, the cooling rate for reducing thesecond post-exposure temperature, the pressure of a gaseous environmentsurrounding the substrate during the elevation of the substrate to thesecond post-exposure temperature, or a composition of the gaseousenvironment surrounding the substrate during the elevation of thesubstrate to the second post-exposure temperature, or a combination oftwo or more thereof; (5) adjusting the composition of the firstchemistry, the time duration for applying the first chemistry, or atemperature of the first chemistry, or a combination of two or morethereof; or (6) adjusting the composition of the second chemistry, thetime duration for applying the second chemistry, or a temperature forthe second chemistry, or a combination of two or more thereof; or (7)performing a combination of two or more thereof.

Referring now to FIG. 6, a flow chart 600 of a method for doublepatterning a substrate is presented according to an embodiment. Flowchart 600 begins in 610 when a layer of radiation-sensitive material isformed on a substrate and, in 620, the layer of radiation-sensitivematerial is exposed to a pattern of radiation using a mask having a maskcritical dimension to form first radiation-sensitive material portionshaving a high radiation exposure, second radiation-sensitive materialportions having a low radiation exposure, and third radiation-sensitivematerial portions having an intermediate radiation exposure.

In 630, the first radiation-sensitive material portions are removed fromthe substrate by performing positive-tone developing of the layer ofradiation-sensitive material from the substrate using a first chemistry.The removal of the first radiation-sensitive material portions may becharacterized by a first critical dimension, or positive-tone criticaldimension. The positive-tone development process may comprise setting acomposition of the first chemistry, a time duration for the firstdevelopment process, or a temperature for the first development process,or any combination of two or more thereof. The first chemistry maycomprise a base solution. The first chemistry may further comprise abase solution, water, and an optional surfactant.

In 640, a temperature of the substrate is elevated to a firstpost-exposure temperature. The thermal treatment process may comprise afirst post-exposure bake (PEB). The first PEB proceeds after theexposing and before the positive-tone developing of the layer ofradiation-sensitive material. The first PEB may comprise setting thefirst post-exposure temperature, a time the substrate is elevated to thefirst post-exposure temperature, a heating rate for achieving the firstpost-exposure temperature, a cooling rate for reducing the firstpost-exposure temperature, a pressure of a gaseous environmentsurrounding the substrate during the elevation of the substrate to thefirst post-exposure temperature, or a composition of a gaseousenvironment surrounding the substrate during the elevation of thesubstrate to the first post-exposure temperature, or a combination oftwo or more thereof.

In 650, the second radiation-sensitive material portions are removedfrom the substrate by performing negative-tone developing of the layerof radiation-sensitive material from the substrate using a secondchemistry. The removal of the second radiation-sensitive materialportions may be characterized by a second critical dimension, ornegative-tone critical dimension. The negative-tone development processmay comprise setting a composition of the second chemistry, a timeduration for the negative-tone development process, or a temperature forthe negative-tone development process, or any combination of two or morethereof. The second chemistry may comprise an organic solvent. Thesecond chemistry may further comprise an organic solvent, water, and anoptional surfactant.

In 660, a temperature of the substrate is elevated to a secondpost-exposure temperature. The thermal treatment process may comprise asecond post-exposure bake (PEB). The second PEB proceeds after thepositive-tone developing of the layer of radiation-sensitive materialand before the negative-tone developing of the layer ofradiation-sensitive material. The second PEB may comprise setting thesecond post-exposure temperature, a time the substrate is elevated tothe second post-exposure temperature, a heating rate for achieving thesecond post-exposure temperature, a cooling rate for reducing the secondpost-exposure temperature, a pressure of a gaseous environmentsurrounding the substrate during the elevation of the substrate to thesecond post-exposure temperature, or a composition of a gaseousenvironment surrounding the substrate during the elevation of thesubstrate to the second post-exposure temperature, or a combination oftwo or more thereof.

The features remaining on the substrate occupy regions related to thethird radiation-sensitive material regions (subject to intermediateradiation exposure) may be characterized by a third critical dimension.

In 670, the third critical dimension is adjusted, controlled and/oroptimized to meet pre-specified pattern requirements that may include apre-specified third critical dimension. This adjusting, controllingand/or optimizing include altering the patterning process.

The adjusting of the patterning process to achieve a target thirdcritical dimension comprises: the use of and the adjustment, controland/or optimization of the second post-exposure bake. The second PEB maybe adjusted by: adjusting the second post-exposure temperature, the timethe substrate is elevated to the second post-exposure temperature, theheating rate for achieving the second post-exposure temperature, thecooling rate for reducing the second post-exposure temperature, thepressure of a gaseous environment surrounding the substrate during theelevation of the substrate to the second post-exposure temperature, or acomposition of the gaseous environment surrounding the substrate duringthe elevation of the substrate to the second post-exposure temperature,or a combination of two or more thereof.

According to one example, as will be illustrated below, the secondcritical dimension, or negative-tone critical dimension (associated withnegative-tone developing) may be increased by the mere addition of thesecond thermal treatment step and the elevation of the substrate to thesecond post-exposure temperature for a period of time. In this example,following the exposure to the pattern of radiation, the substrate iselevated to the first post-exposure temperature, followed bypositive-tone developing, followed by elevating the substrate to thesecond post-exposure temperature, followed by negative-tone developing.The second post-exposure temperature should be sufficiently high tocause chemical modification of the layer of radiation-sensitive materialremaining on the substrate prior to negative-tone developing.Additionally, an increase in the second post-exposure temperature maycause a further increase in the second critical dimension. When holdingthe first critical dimension or positive-tone critical dimensionapproximately constant, the third critical dimension may also beincreased with the second PEB and an increase in the secondpost-exposure temperature.

According to another example, the first critical dimension, orpositive-tone critical dimension (associated with positive-tonedeveloping) may be increased by the addition of the second thermaltreatment step and the elevation of the substrate to the secondpost-exposure temperature for a period of time. In this example,following the exposure to the pattern of radiation, the substrate iselevated to the first post-exposure temperature, followed bynegative-tone developing, followed by elevating the substrate to thesecond post-exposure temperature, followed by positive-tone developing.The second post-exposure temperature should be sufficiently high tocause chemical modification of the layer of radiation-sensitive materialremaining on the substrate prior to positive-tone developing.Additionally, an increase in the second post-exposure temperature maycause a further increase in the first critical dimension. When holdingthe second critical dimension or negative-tone critical dimensionapproximately constant, the third critical dimension may also bedecreased with the second PEB and an increase in the secondpost-exposure temperature.

Referring now to FIG. 7, a flow chart 700 of a method for doublepatterning a substrate is presented according to an embodiment. Flowchart 700 begins in 710 when a layer of radiation-sensitive material isformed on a substrate and, in 720, the layer of radiation-sensitivematerial is exposed to a pattern of radiation using a mask having a maskcritical dimension to form first radiation-sensitive material portionshaving a high radiation exposure, second radiation-sensitive materialportions having a low radiation exposure, and third radiation-sensitivematerial portions having an intermediate radiation exposure.

In 730, the first radiation-sensitive material portions are removed fromthe substrate by performing positive-tone developing of the layer ofradiation-sensitive material from the substrate using a first chemistry.The removal of the first radiation-sensitive material portions may becharacterized by a first critical dimension, or positive-tone criticaldimension. The positive-tone development process may comprise setting acomposition of the first chemistry, a time duration for the firstdevelopment process, or a temperature for the first development process,or any combination of two or more thereof. The first chemistry maycomprise a base solution. The first chemistry may further comprise abase solution, water, and an optional surfactant.

Optionally, a temperature of the substrate is elevated to a firstpost-exposure temperature. The thermal treatment process may comprise afirst post-exposure bake (PEB). The first PEB proceeds after theexposing and before the positive-tone developing of the layer ofradiation-sensitive material. The first PEB may comprise setting thefirst post-exposure temperature, a time the substrate is elevated to thefirst post-exposure temperature, a heating rate for achieving the firstpost-exposure temperature, a cooling rate for reducing the firstpost-exposure temperature, a pressure of a gaseous environmentsurrounding the substrate during the elevation of the substrate to thefirst post-exposure temperature, or a composition of a gaseousenvironment surrounding the substrate during the elevation of thesubstrate to the first post-exposure temperature, or a combination oftwo or more thereof.

In 740, the second radiation-sensitive material portions are removedfrom the substrate by performing negative-tone developing of the layerof radiation-sensitive material from the substrate using a secondchemistry. The removal of the second radiation-sensitive materialportions may be characterized by a second critical dimension, ornegative-tone critical dimension. The negative-tone development processmay comprise setting a composition of the second chemistry, a timeduration for the negative-tone development process, or a temperature forthe negative-tone development process, or any combination of two or morethereof. The second chemistry may comprise an organic solvent. Thesecond chemistry may further comprise an organic solvent, water, and anoptional surfactant.

Optionally, a temperature of the substrate is elevated to a secondpost-exposure temperature. The thermal treatment process may comprise asecond post-exposure bake (PEB). The second PEB proceeds after thepositive-tone developing of the layer of radiation-sensitive materialand before the negative-tone developing of the layer ofradiation-sensitive material. The second PEB may comprise setting thesecond post-exposure temperature, a time the substrate is elevated tothe second post-exposure temperature, a heating rate for achieving thesecond post-exposure temperature, a cooling rate for reducing the secondpost-exposure temperature, a pressure of a gaseous environmentsurrounding the substrate during the elevation of the substrate to thesecond post-exposure temperature, or a composition of a gaseousenvironment surrounding the substrate during the elevation of thesubstrate to the second post-exposure temperature, or a combination oftwo or more thereof.

The features remaining on the substrate occupy regions related to thethird radiation-sensitive material regions (subject to intermediateradiation exposure) may be characterized by a third critical dimension.

In 750, the third critical dimension is adjusted, controlled and/oroptimized to meet pre-specified pattern requirements that may include apre-specified third critical dimension. This adjusting, controllingand/or optimizing include altering the patterning process.

The adjusting of the patterning process to achieve a target thirdcritical dimension comprises: the adjustment, control and/oroptimization of the positive-tone developing. The positive-tonedeveloping may be adjusted by: adjusting the composition of the firstchemistry, the time duration for applying the first chemistry, or atemperature of the first chemistry, or a combination of two or morethereof.

According to one example, as will be illustrated below, the firstcritical dimension, or positive-tone critical dimension (associated withpositive-tone developing) may be decreased by an adjustment of thecomposition of the first chemistry. When the first chemistry comprises abase with water and an optional surfactant, the dilution of the base inthe solution may cause a decrease in the first critical dimension. Whenholding the second critical dimension or negative-tone criticaldimension approximately constant, the third critical dimension may alsobe increased with the dilution of the positive-tone developing solution.

Referring now to FIG. 8, exemplary data 800 is provided for a dual-tonedouble patterning process. As illustrated in FIG. 8, the printedcritical dimension (nm, nanometers) is provided as a function ofexposure dose (mJ/cm², milli-Joules per square centimeters) for a set ofnegative-tone development characteristics 810 and a set of positive-tonedevelopment characteristics 820. The set of negative-tone developmentcharacteristics 810 and the set of positive-tone developmentcharacteristics 820 may be acquired using numerical simulation,experiment, or a combination thereof.

A characteristic defines a relationship between a critical dimension anda control parameter, such as an exposure dose; however, other controlparameters may be used. The characteristic is determined by setting aset of process parameters for performing the dual-tone patterningprocess, such as the processes described in FIGS. 3, 4A-4D, 5, 6, and 7,wherein the set of process parameters includes any one or more of theprocess parameters described above with respect to these processes.While holding these process parameters constant, a critical dimension ismeasured and/or computed as the control parameter is varied. Thisprocedure for preparing a characteristic may be used to determine one ormore negative-tone characteristics and/or one or more positive-tonecharacteristics. The characteristics may be prepared using anegative-tone pattern development process, a positive-tone patterndevelopment process, or a dual-tone pattern development process.

The set of negative-tone development characteristics 810 exhibit avariation in one or more parameters useful in adjusting or controllingthe negative-tone critical dimension. For example, the one or moreparameters may include any parameter, as described above, for performinga second post-exposure bake following the positive-tone development.Additionally, for example, the one or more parameters may include anyparameter for performing the negative-tone development.

As shown in FIG. 9, a film thickness (nm) (or normalized film thickness)for a layer of radiation-sensitive material following negative-tonedevelopment is shown as a function of exposure dose (mJ/cm²). A firstcontrast curve 910 in the exemplary data 900 is presented wherein thesecond post-exposure bake following positive-tone development is notperformed. A second set of curves 920 are also presented wherein thesecond post-exposure bake following positive-tone development isperformed. As depicted in FIG. 9, the contrast curves shift to lowerexposure dose (indicated by arrow 930) indicating a decrease in thelower solubility threshold or a resulting increase in the negative-tonecritical dimension. The shift to lower exposure dose of the negativecontrast curves may be achieved by increasing the second post-exposuretemperature and/or the time duration for elevation at the secondpost-exposure temperature (see trend 814 in FIG. 8).

In FIG. 8, the set of positive-tone development characteristics 820exhibit a variation in one or more parameters useful in adjusting orcontrolling the positive-tone critical dimension. For example, the oneor more parameters may include any parameter, as described above, forperforming a second post-exposure bake following the positive-tonedevelopment. Additionally, for example, the one or more parameters mayinclude any parameter for performing the positive-tone development.

As shown in FIG. 10, a film thickness (nm) (or normalized filmthickness) for a layer of radiation-sensitive material followingpositive-tone development is shown as a function of exposure dose(mJ/cm²). A first set of positive contrast curves 1010 in exemplary data1000 is provided having a first contrast curve 1012 and a secondcontrast curve 1014. The first contrast curve 1012 is acquired when thesecond post-exposure bake following positive-tone development is notperformed. The second contrast curve 1014 is acquired when the secondpost-exposure bake following positive-tone development is not performedand the positive-tone development solution (e.g., first chemistry havinga base, water, and optional surfactant) is diluted relative to the firstcontrast curve 1012. As depicted in FIG. 10, the contrast curves shiftto higher exposure dose (indicated by arrow 1030) indicating an increasein the upper solubility threshold or a resulting decrease in thepositive-tone critical dimension. The shift to higher exposure dose ofthe positive contrast curves may be achieved by increasing the dilutionof the positive-tone development chemistry (see trend 824 in FIG. 8).

A second set of curves 1020 is provided having a third contrast curve1022 and a fourth contrast curve 1024. The third contrast curve 1022 isacquired when the second post-exposure bake following positive-tonedevelopment is performed and the positive-tone development solution isthe same for the first contrast curve 1012. As depicted in FIG. 10, thecontrast curves shift to lower exposure dose (indicated by arrow 1040)indicating a decrease in the upper solubility threshold or a resultingincrease in the positive-tone critical dimension. The shift to lowerexposure dose of the positive contrast curves may be achieved byincreasing the second post-exposure temperature and/or the time durationfor elevation at the second post-exposure temperature.

The fourth contrast curve 1024 is acquired when the second post-exposurebake following positive-tone development is performed and thepositive-tone development solution is diluted relative to the firstcontrast curve 1012. As depicted in FIG. 10, the contrast curves shiftto higher exposure dose (indicated by arrow 1030) indicating an increasein the upper solubility threshold or a resulting decrease in thepositive-tone critical dimension.

As shown in FIG. 11, a film thickness (nm) (or normalized filmthickness) for a layer of radiation-sensitive material followingnegative-tone development is shown as a function of exposure dose(mJ/cm²). Following the exposure of the layer of radiation-sensitivematerial to a pattern of radiation, the layer of radiation-sensitivematerial undergoes a first post-exposure bake for a first time durationfollowed by positive-tone development, and then undergoes a secondpost-exposure bake for a second time duration followed by negative-tonedevelopment. A family of contrast curves 1110 in the exemplary data 1100is presented, wherein the first time duration for the firstpost-exposure bake (e.g., the first time duration is indicated in thelegend by the time preceding “POS”) and the second time duration for thesecond post-exposure bake (e.g., the second time duration is indicatedin the legend by the time preceding “NEG”) are varied.

As illustrated in FIG. 11, when the first time duration for the firstpost-exposure bake (preceding the positive-tone development) is heldconstant (i.e., at 25 sec (seconds), 35 sec, and 45 sec) while thesecond time duration for the second post-exposure bake (preceding thenegative-tone development) is increased (i.e., 35 sec to 95 sec, 25 secto 85 sec, and 15 sec to 75 sec), the lower exposure threshold shifts tothe left (i.e., the lower exposure threshold decreases) (trend indicatedby arrow 1140). The decrease in the lower exposure threshold manifestsas an increase in the second critical dimension or negative-tonecritical dimension. Furthermore, while the lower exposure threshold isdecreased by increasing the second time duration during the secondpost-exposure bake, the upper exposure threshold remains substantiallyconstant when the first time duration is held constant.

Additionally, as illustrated in FIG. 11, when the second time durationfor the second post-exposure bake (preceding the negative-tonedevelopment) is held approximately constant with a slight variation(i.e., at 35 sec, 25 sec, and 15 sec; and at 95 sec, 85 sec, and 75 sec)while the first time duration for the first post-exposure bake(preceding the positive-tone development) is increased (i.e., 35 sec to35 sec to 45 sec), the upper exposure threshold shifts to the left(i.e., the upper exposure threshold decreases) (trend indicated by arrow1130). The decrease in the upper exposure threshold manifests as anincrease in the first critical dimension or positive-tone criticaldimension. Furthermore, while the upper exposure threshold is decreasedby increasing the first time duration during the first post-exposurebake, the lower exposure threshold remains approximately constant whenthe second time duration is held approximately constant.

Referring again to FIG. 8, when printing a pattern of features on asubstrate, a target positive-tone critical dimension (CD_(POS)) and atarget negative-tone critical dimension (CD_(NEG)) may be selected orspecified. Thereafter, a target difference (T_(DD)) between the targetpositive-tone critical dimension and the target negative-tone criticaldimension may be computed for the double development metric.Alternatively, two or more of the target difference, the targetpositive-tone critical dimension and the target negative-tone criticaldimension may be specified, while the third is computed.

Through inspection of the set of negative-tone developmentcharacteristics 810 and the set of positive-tone developmentcharacteristics 820, a target negative-tone characteristic 812 may beselected and a target positive-tone characteristic 822 may be selectedthat possesses a ΔCD_(NP) comparable to T_(DD). Desirably, the selectedcharacteristics possess a ΔCD_(NP) that is greater than T_(DD).

The dual-tone double patterning process may be optimized by selectingthe target negative-tone characteristic and the target positive-tonecharacteristic such that the target positive-tone characteristicintersects the target positive-tone critical dimension at a givenexposure dose and the target negative-tone characteristic intersects thetarget negative-tone critical dimension at the same given exposure dose.

Alternatively, the dual-tone double patterning process may be optimizedby selecting the target positive-tone characteristic such that thetarget positive-tone characteristic intersects the target positive-tonecritical dimension at a given exposure dose. Then, the targetnegative-tone characteristic may be selected when ΔCD_(NP) isapproximately comparable to T_(DD) for the given exposure dose.Alternatively yet, the target negative-tone characteristic may beselected when DDM is approximately unity, where:

DDM=1−([|ΔCD _(NP) |−T _(DD) ]/T _(DD)).  (3)

Referring now to FIG. 12, a flow chart 1200 of a method for optimizing adouble patterning process is presented according to an embodiment. Flowchart 1200 begins in 1210 with performing a dual-tone developmentprocess. The dual-tone development process comprises: exposing a layerof radiation-sensitive material to a pattern of radiation, performing apositive-tone development process to remove a first radiation-sensitivematerial portion characterized by a positive-tone critical dimension,and performing a negative-tone development process to remove a secondradiation-sensitive material portion characterized by a negative-tonecritical dimension.

In 1220, the dual-tone development process is optimized to achieve atarget difference between a target positive-tone critical dimension anda target negative-tone critical dimension. The optimization of thedual-tone development process comprises: acquiring one or morepositive-tone characteristics, wherein the one or more positive-tonecharacteristics relate the positive-tone critical dimension to a controlparameter for a first set of process parameters; acquiring one or morenegative-tone characteristics, wherein the one or more negative-tonecharacteristics relate the negative-tone critical dimension to thecontrol parameter for a second set of process parameters; selecting atarget positive-tone characteristic from the one or more positive-tonecharacteristics that approximately intersects the target positive-tonecritical dimension at a target control parameter to within a firstdeviation; selecting a target negative-tone characteristic from the oneor more negative-tone characteristics that approximately intersects thetarget negative-tone critical dimension at the target control parameterto within a second deviation; and establishing a process recipe for theperforming the dual-tone development process using the targetpositive-tone characteristic, the target negative-tone characteristic,and the target control parameter.

The first deviation and the second deviation may be selected to be anabsolute value, such as plus or minus 5 nm, plus or minus 2 nm.Alternatively, first deviation and the second deviation may be selectedto be an relative value, such as plus or minus 10% of T_(DD), plus orminus 5% Of T_(DD).

Although only certain embodiments of this invention have been describedin detail above, those skilled in the art will readily appreciate thatmany modifications are possible in the embodiments without materiallydeparting from the novel teachings and advantages of this invention. Forexample, several embodiments are described herein that use a singleexposure of a layer of radiation-sensitive material to a pattern ofradiation. However, a plurality of exposures may be utilized.Accordingly, all such modifications are intended to be included withinthe scope of this invention.

1. A method of optimizing a double patterning process, comprising: performing a dual-tone development process that includes: exposing a layer of radiation-sensitive material to a pattern of radiation, performing a positive-tone development process to remove a first radiation-sensitive material portion characterized by a positive-tone critical dimension, and performing a negative-tone development process to remove a second radiation-sensitive material portion characterized by a negative-tone critical dimension; and optimizing said dual-tone development process to achieve a target difference between a target positive-tone critical dimension and a target negative-tone critical dimension by: acquiring one or more positive-tone characteristics, said one or more positive-tone characteristics relate said positive-tone critical dimension to a control parameter for a first set of process parameters; acquiring one or more negative-tone characteristics, said one or more negative-tone characteristics relate said negative-tone critical dimension to said control parameter for a second set of process parameters; selecting a target positive-tone characteristic from the one or more positive-tone characteristics that approximately intersects the target positive-tone critical dimension at a target control parameter to within a first deviation; selecting a target negative-tone characteristic from the one or more negative-tone characteristics that approximately intersects the target negative-tone critical dimension at the target control parameter to within a second deviation; and establishing a process recipe for said performing said dual-tone development process using said target positive-tone characteristic, said target negative-tone characteristic, and said target control parameter.
 2. The method of claim 1, wherein said layer of radiation-sensitive material comprises a photo-resist.
 3. The method of claim 1, wherein said layer of radiation-sensitive material comprises a 248 nm photo-resist, a 193 nm photo-resist, a 157 nm photo-resist, or an extreme ultraviolet photo-resist, or a combination of two or more thereof.
 4. The method of claim 1, wherein said layer of radiation-sensitive material comprises a positive-tone photo-resist.
 5. The method of claim 1, wherein said layer of radiation-sensitive material comprises a dual-tone photo-resist.
 6. The method of claim 1, wherein said layer of radiation-sensitive material comprises a photo-resist that switches solubility due to a change in polarity upon said exposing to said pattern of radiation and said optionally elevating said temperature of said substrate following said exposure.
 7. The method of claim 1, wherein said layer of radiation-sensitive material comprises a photo-resist that provides acid-catalyzed deprotection upon said exposing to said pattern of radiation and said optionally elevating said temperature of said substrate following said exposure.
 8. The method of claim 1, wherein said positive-tone development process is performed prior to said negative-tone development process.
 9. The method of claim 1, wherein said negative-tone development process is performed prior to said positive-tone development process.
 10. The method of claim 1, wherein said positive-tone development process comprises utilizing a base solution, and said negative-tone development process comprises utilizing an organic solvent.
 11. The method of claim 1, further comprising: performing a first post-exposure bake by elevating a temperature of said substrate to a first post-exposure temperature following said exposing and preceding said performing said positive-tone development process.
 12. The method of claim 11, further comprising: performing a second post-exposure bake by elevating a temperature of said substrate to a second post-exposure temperature following said exposing and preceding said performing said negative-tone development process.
 13. The method of claim 1, further comprising: performing a first post-exposure bake by elevating a temperature of said substrate to a first post-exposure temperature following said exposing and preceding said performing said positive-tone development process; and performing a second post-exposure bake by elevating a temperature of said substrate to a second post-exposure temperature following said exposing and preceding said performing said negative-tone development process.
 14. The method of claim 13, wherein said control parameter comprises an exposure dose.
 15. The method of claim 14, wherein said first set of process parameters comprises a first post-exposure temperature for said first post-exposure bake, a time said substrate is elevated to said first post-exposure temperature, a heating rate for achieving said first post-exposure temperature, a cooling rate for reducing said first post-exposure temperature, a pressure of a gaseous environment surrounding said substrate during said elevation of said substrate to said first post-exposure temperature, a composition of a gaseous environment surrounding said substrate during said elevation of said substrate to said first post-exposure temperature, a composition of a first chemistry used during said positive-tone development process, a time duration for applying said first chemistry, or a temperature of said first chemistry, or a combination of two or more thereof.
 16. The method of claim 15, wherein said acquiring said one or more positive-tone characteristics comprises varying one or more process parameters in said first set of process parameters.
 17. The method of claim 15, wherein said acquiring said one or more positive-tone characteristics comprises varying said composition of said first chemistry used during said positive-tone development process.
 18. The method of claim 14, wherein said second set of process parameters comprises a second post-exposure temperature for said second post-exposure bake, a time said substrate is elevated to said second post-exposure temperature, a heating rate for achieving said second post-exposure temperature, a cooling rate for reducing said second post-exposure temperature, a pressure of a gaseous environment surrounding said substrate during said elevation of said substrate to said second post-exposure temperature, a composition of a gaseous environment surrounding said substrate during said elevation of said substrate to said second post-exposure temperature, a composition of a second chemistry used during said negative-tone development process, a time duration for applying said second chemistry, or a temperature of said second chemistry, or a combination of two or more thereof.
 19. The method of claim 15, wherein said acquiring said one or more negative-tone characteristics comprises varying one or more process parameters in said second set of process parameters.
 20. The method of claim 15, wherein said acquiring said one or more negative-tone characteristics comprises varying said second post-exposure temperature for said second post-exposure bake, or said time said substrate is elevated to said second post-exposure temperature, or both. 